1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus, and more specifically to an ultrasonic diagnostic apparatus which can automatically determine the optimum image conditions such as brightness, contrast, etc.
2. Description of the Prior Art
The ultrasonic diagnostic apparatus transmits ultrasonic waves to a living body, receives echoes reflected from the inside of the living body, converts the received echoes to analog echo signals, and displays an image (e.g. tomographic image) on a display unit (e.g. CRT) based on the echo signals.
The ultrasonic waves are transmitted and received from and by an ultrasonic transducer (probe). In this case, the echoes received by the ultrasonic transducer are extremely weak. Therefore, in order to clearly display a tomographic image on the CRT based on the echo signals, it is necessary to amplify the echo signals through a few amplifier circuits. Further, when the tomographic image is displayed on the CRT, it is important to adjust the contrast of the image. Accordingly, the adjustments for the amplification level of the echo signals and the contrast of the displayed image are essential factors to determine the quality of the image of the ultrasonic diagnostic apparatus.
FIG. 1 shows an echo signal amplifier circuit of the prior art ultrasonic diagnostic apparatus. In the drawing, analog echo signals fed from an ultrasonic transducer 1 are first inputted to a gain circuit 2. The echo signals are amplified by the gain circuit 2. The amplification factor of the gain circuit 2 is determined in response to a gain signal 500 whose level can be adjusted by a dial which is rotatable manually.
The amplified echo signals are then inputted to a STC (sensitivity time control) circuit 4. This STC circuit 4 amplifies the echo signals on the basis of respective different amplification factors determined according to the respective visual field depths in the ultrasonic beam direction. In other words, STC signals 502 which are applied to the STC circuit 4 are determined for each visual field depth, so that the amplification level of the echo signals are adjusted for each visual field depth according to the level of each STC signal 502.
In the prior art ultrasonic diagnostic apparatus, however, a plurality of sliders (e.g. 16 sliders) are arranged on a control panel, so that the levels of the STC signals 502 can be adjusted manually by operating the sliders. Therefore, it has been performed to selectively increase the brightness of only the image obtained at a specific depth (from which a weak echo is received), for instance. The echo signals from the STC circuit 4 are then fed to a logarithmic amplifier 5 and amplified logarithmically, that is to say, low level signals therein are mainly amplified.
Successively, the echo signals from the logarithmic amplifier 5 are inputted to a contrast circuit 6. This contrast circuit 6 adjusts the image contrast of the echo signals according to a contrast signal 504 inputted thereto. Here, when the brightness levels of the respective pixels (picture elements) on a single image obtained on the basis of the echo signals are arranged in a histogram fashion, it is possible to adjust the slope of the obtained histogram sharply or gently, by adjusting the level of the contrast signal 504. In practice, when the slope of the convex portion of the histogram is made sharp, the image becomes dim since this indicates that the brightness levels of the respective pixels concentrate, relatively. On the other hand, when the slope of the convex portion of the histogram is made flat, the image becomes strong in light and shade since this indicates that the brightness levels of the respective pixels scatter, relatively. In the prior art ultrasonic diagnostic apparatus, the image contrast is adjusted by adjusting the level of the contrast signal 504 by operating a dial provided on the control panel manually.
The echo signals 506 outputted from the contrast circuit 6 are applied to an A/D converter 7, so that the applied echo signals 506 are converted into digital signals through the A/D converter 7. The converted digital signals 508 are transmitted to a frame memory 8, and then converted into analog signals and displayed on a monitor 9 (e.g. CRT).
In the prior art ultrasonic diagnostic apparatus as described above, in order to manually obtain an ultrasonic image under the optimum image conditions (e.g. with respect to brightness and contrast), it is necessary to adjust the levels of the gain signal 500, the STC signal 502 for each visual field depth, and the contrast signal 504. However, since these adjustment levels of these signals 500, 502, 504 are different according to various conditions such as the part of a living body, the thickness of the layer of body fat, the figure of the body, etc. the adjustments of the levels are very delicate and fine. Therefore, there exists a problem in that the operator must rotate the dials in trial and error fashion repeatedly and therefore the adjustment operation is complicated. In addition, when the gains of a plurality of visual field depth areas are required to be adjusted, there exists a further problem in that the manual adjustment operation requires further long time because the balance between the mutual brightness levels in the respective visual field depth areas is also required. Further, in the ultrasonic diagnostic apparatus, in particular the image quality and visibility exert a serious influence upon the precision in disease diagnosis, and additionally it is extremely desirable to diagnose a part of a patient in a time as short as possible in the case of the ultrasonic diagnosis during an operation. In other words, there exists a need of an ultrasonic diagnostic apparatus which can provide the optimum images under the best image conditions automatically and momentarily.